A thrust roller bearing such as disclosed in JP 2005-164023 (A) is installed in rotational support sections of various kinds of rotary machinery such as the transmission of an automobile, and while supporting thrust loads that are applied between a rotating member, such as a rotating shaft, and a stationary member, such as a casing, allows the rotating member to rotate. Moreover, in the case where a pair of members that rotate relative to each other by way of this kind of thrust roller bearing are made of a material, the required hardness of which is difficult to maintain, or in the case where processing the material to a required smoothness is difficult or troublesome, a thrust roller bearing with races that combines one cage and a plurality of rollers with two races is used.
FIG. 7 illustrates an example of a conventionally known thrust roller bearing with races 1. This thrust bearing with races 1 has a plurality of rollers 2 that are arranged in a radial direction, a cage 3 that holds these rollers 2, and a first thrust race 4 and second thrust race 5 that hold the cage 3 from both sides in the axial direction. The cage 3 is formed completely in a circular ring shape, and the same number of pockets 6 as the rollers 2 is provided in the cage 3 so as to be radially arranged at regular intervals in the circumferential direction.
Moreover, the first thrust race 4 and second thrust race 5 are both made using a sufficiently hard metal plate such as bearing steel or case hardening steel, and formed by punching and bending with a press. Typically, the first thrust race 4, which is called as an outer race, has a flat, circular ring-shaped first thrust race section 7, and a cylindrical-shaped outer-diameter side flange 8 that is provided so as to be bent to one side in the axial direction from the outer circumferential edge of the first thrust race section 7. An outer-diameter side locking section 9 that is bent inward in the radial direction is provided on the tip-end edge of the outer-diameter side flange 8. On the other hand, the second thrust race 5, which is typically called an inner race, has a flat, circular ring-shaped second thrust race section 10, and a cylindrical-shaped inner-diameter flange 11 that is provided so as to be bent to one side in the axial direction from the inner-circumferential edge of the second thrust race section 10. An inner-diameter side locking section 12 that is bent outward in the radial direction is provided on the tip-end edge of the inner-diameter side flange 11.
The inner diameter of the outer-diameter side flange 8 is larger than the outer diameter of the cage 3, the outer diameter of the inner-diameter side flange 11 is smaller than the inner diameter of the cage 3, and the cage 3 can be placed between the outer-diameter side flange 8 and inner-diameter side flange 11 so as to be able to rotate relative to the first thrust race 4 and second thrust race 5. The diameter of the inscribed circle of the outer-diameter side locking section 9 is a little smaller than the outer diameter of the cage 3, and the diameter of the circumscribed circle of the inner-diameter side locking section 12 is a little larger than the inner diameter of this cage 3. The cage 3 that holds the roller 2 is combined with the first thrust race 4 and second thrust race 5 while elastically deforming the outer-diameter side flange 8 and inner-diameter side flange 11, and after being combined, these members are capable of relative rotation, and are prevented from accidentally separating from each other. In the example in the figure, it is taken into consideration that the first thrust race 4 is mounted on a ferrous alloy member having high hardness and the second thrust race 5 is mounted on an aluminum alloy member having low hardness. Therefore, the thickness dimension of the second thrust race 5 is greater than the thickness dimension of the first thrust race 4.
The thrust roller bearing with races 1 that is constructed in this way, as illustrated in FIG. 8, is mounted in the rotational support section where thrust loads occur with the outer-diameter side flange 8 that is formed around the outer-circumferential edge of the first thrust race 4 fitted inside a support section 14 that is formed in the casing 13. Moreover, the second thrust race 5 comes in contact with the end surface of an opposing member 15. In this state, this opposing member 15 is supported by the casing 13 so as to be able to freely rotate. The thrust roller bearing with races 1 supports the thrust load that is applied between the opposing member 15 and the casing 13. It is desired that in this kind of thrust roller bearing with races 1, the following functions (1) to (4) should all be achieved to a high degree as much as possible.
(1) The cage 3, first thrust race 4 and second thrust race 5 should not accidentally separate.
This function is necessary in order to prevent not being able to obtain the original performance of the thrust roller bearing with races 1, and to prevent the assembly work of a transmission or the like from becoming troublesome due to these members becoming separated from the time of transport from the factory where the thrust roller bearing with races 1 is manufactured to the assembly factory of the transmission or the like until the time when assembled in a specified portion.
(2) During operation of a transmission or the like, it should be possible to maintain the amount of flow of lubricant (lubricant flow amount) that flows in the internal space between the first thrust race 4 and second thrust race 5 where the cage 3 and rollers 2 are located.
This function is required in order to maintain the strength of the oil film that is formed in the areas of rolling contact between the rolling surfaces of the rollers 2 and the first thrust race section 7 and second thrust race section 10 during operation of the transmission or the like, as well as to effectively cool those areas of rolling contact.
(3) Relative rotation of the cage 3 to the first thrust race 4 and second thrust race 5 should be assured even when the centers of rotation of the first thrust race 4 and second thrust race 5 are shifted a little (i.e. when the operation of these thrust races is a little eccentric).
This function is necessary in order to maintain the functions of the thrust roller bearing with races 1 even when, due to manufacturing error or assembly error of the thrust roller bearing with races 1, the transmission or the like, the centers of rotation of the first thrust race 4 and second thrust race 5 are shifted a little.
(4) The thrust roller bearing with races 1 should be able to be assembled in only a specified direction with respect to the casing 13 (i.e. should not be able to be assembled in the reverse direction).
This function is necessary in order to prevent the occurrence of damage such as burning of the thrust roller bearing with races 1 due to the flow path for the lubricant becoming blocked because the thrust roller bearing with races 1 is assembled in the reverse direction.
In the case of the conventional construction, it is difficult to achieve all of the functions given in (1) to (4) above to a high degree, so there is a disadvantage in attempting to improve the function of various machines in which this kind of thrust roller bearing with races is assembled. This will be explained below.
In order to achieve the functions (1) and (2) to a high degree, it is necessary to widen the space that exists between the outer-diameter side flange 8 and inner-diameter side flange 11 and both the inside and outside circumferential surfaces of the cage while at the same time increasing the engagement amount between the outer-diameter side locking section 9 and inner-diameter side locking section 12 and the circumferential edge of the cage 3. However, taking into consideration the ease of assembling the first thrust race 4, second thrust race 5 and cage 3, it is not possible to increase the engagement amount in excess. For example, when assembling the cage 3 and first thrust race 4, the outer circumferential edge section of the cage 3 is placed on the outer-diameter side locking section 9 while at the same time elastically deforming the outer-diameter side flange 8 outward in the radial direction such as illustrated in FIGS. 9A→9B→9C. This work becomes difficult when the protruding amount δ that the outer-diameter side locking section 9 protrudes from the inner circumferential surface of the outer-diameter side flange 8 becomes too large.
As the outer-diameter side locking section 9, there is so-called full curl construction that is obtained by bending the tip-end edge section of the outer-diameter side flange 8 inward in the radial direction around the entire circumference, and there is so-called partial curl construction that is obtained by bending the tip-end edge of the outer-diameter side flange 8 inward in the radial direction at a plurality of locations that are spaced intermittently in the circumferential direction. In the case of full curl construction, the cage 3 will not be able to assembled inside the outer-diameter side flange 8 unless the protruding amount δ is made considerably small, or the outer diameter of the cage 3 is made considerably less than the inner diameter of the outer-diameter side flange 8 in case of maintaining this protruding amount δ. However, making the outer diameter of the cage 3 too much smaller than the inner diameter of the outer-diameter side flange 8 is not preferable from the aspect of maintaining the ability to position the cage 3 in the radial direction with respect to the first thrust race 4 (i.e. suppressing run-out in the radial direction of the cage 3). Therefore, in the case of employing full curl construction, it is necessary to make the protruding amount δ small. In the case of using full curl construction of the outer-diameter side locking section 9 in a thrust roller bearing with races 1 having the outer diameter of the outer-diameter side flange of 60 mm to 120 mm and the inner diameter of the inner-diameter side flange of 40 mm to 80 mm, which is a subject of the present invention, when the protruding amount δ is greater than 0.4 mm, it becomes difficult to assemble the cage 3 inside the outer-diameter side flange 8.
On the other hand, when partial curl construction is employed, it is possible to increase the amount of elastic deformation of the outer-diameter side flange 8 (i.e. increase the range of elastic deformation) when assembling the cage 3 inside the outer-diameter side flange 8. Therefore, even though the protruding amount δ of the outer-diameter side locking section 9 is made large, and the difference between the outer diameter of the cage 3 and the inner diameter of the outer-diameter side flange 8 is made somewhat small, the cage 3 can be assembled inside the outer-diameter side flange 8 with no particular problem. When outer-diameter side locking sections having partial curl construction are formed at a plurality of locations in the circumferential direction of the tip-end edge of the outer-diameter side flange as disclosed and illustrated in FIG. 3 and FIG. 4 of JP 2008-039031 (A), and of this outer-diameter side flange, the height dimension in the axial direction of the portion between adjacent outer-diameter side locking sections in the circumferential direction is made small, the area of the opening of the internal space between the first thrust race and second thrust race where the cage and rollers are located is made large, and thus it is possible to maintain the amount of lubricant flow and achieve functions (1) and (2) above.
However, even in the construction disclosed and illustrated in FIG. 3 and FIG. 4 of JP 2008-039031 (A), it is not possible to achieve functions (3) and (4). For example, in order to obtain function (3), it is necessary for construction to allow a certain amount (i.e. an appropriate amount, not an excessive amount) of relative displacement in the radial direction between the first thrust race 4 and second thrust race 5 of the thrust roller bearing with races 1. In other words, with the first thrust race 4 and second thrust race 5 supported by a pair of members so as to be able to rotate relative to each other, the races will rotate together with these members. Therefore, when the centers of rotation of these members shift in the radial direction, the first thrust race 4 and second thrust race 5 will have a whirling motion with respect to each other. As illustrated in FIG. 10, as the radius (eccentricity) of this whirling motion becomes large, part of the cage 3 is strongly held between the inner circumferential surface of the outer-diameter side flange 8 and the outer circumferential surface of the inner-diameter side flange 11 (“wedging” of the cage occurs). As a result, a large radial load is applied to part of the cage 3, and it becomes easy for damage such as breaking or cracking of the cage 3 to occur. Moreover, the cage 3 stops rotating, and revolution and rotation of the rollers 2 becomes impossible, and thus the rolling surfaces of the roller 2 rub against or is in sliding contact with the first thrust race surface 17 of the first thrust race section 7 and the second thrust race surface 20 of the second thrust race section 10, and thus in the thrust roller bearing with races 1, burning occurs in the areas of contact between the first thrust race surface 17 and second thrust race surface 20 and the rolling surfaces of the rollers 2, or severe damage such as damage to the cage 3 occurs.
In the case of the thrust roller bearing with races 1 having the outer diameter of the outer-diameter side flange of 60 mm to 120 mm and the inner diameter of the inner-diameter side flange of 40 mm to 80 mm, which is a subject of the present invention, when full curl construction is employed for the outer-diameter side locking section 9, and the inner-diameter side of this outer-diameter side locking section can pass the cage 3, then as described above, the amount of protrusion in the radial direction of this outer-diameter side locking section 9 must be kept to about 0.4 mm. Under this condition, when the internal space in the thrust roller bearing with races 1 stops at about 0.6 mm to 1.6 mm, and shifting in the radial direction of the centers of rotation of these members (i.e. radius of the whirling motion) exceeds 0.5 mm, the possibility that damage such as described above will occur increases. JP 2008-039031 (A) does not disclose construction for preventing such damage.
Moreover, when assembling the thrust roller bearing with races 1 between the casing 13 and opposing member 15, when a mistake is made in the assembly direction, there is a possibility that durability will become poor due to poor lubrication, and sufficient performance of the thrust roller bearing with races 1 will not be able to be obtained. In other words, the thrust roller bearing with races 1 can be assembled in the casing 13 in a direction opposite the proper state illustrated in FIG. 8 (i.e. in an improper state). However, when assembled in the improper state, the first thrust race 4 blocks the space 16 between the casing 13 and the opposing member 15, impairing the flow of lubricant to the inside of the thrust roller bearing with races 1.
As construction for preventing such problems due to assembly in the reverse direction, construction is disclosed and illustrated in FIG. 11 and FIG. 12 of JP 2004-028342 (A) in which the outer diameter of the second thrust race section of the second thrust race is larger than the outer diameter of the outer-diameter side flange of the first thrust race. With this kind of construction, the second thrust race cannot be inserted inside the support section of the casing, so the second thrust race can be prevented from being assembled in the wrong direction in the support section of the casing. In other words, only the first thrust race that is supposed to fit inside this support section can be assembled, so reverse assembly can be prevented. However, in the case of this kind of conventional construction, the section of the second thrust race that is near the outer circumferential edge and that protrudes outward in the radial direction further than the outer circumferential surface of the outer-diameter side flange blocks the opening on the outer-diameter side of the internal space of the thrust roller bearing with races, which reduces the amount of flow of lubricant, so the function (2) is impaired.
As can be understood from the explanation above, in the case of conventional construction, it is difficult to achieve together all of the functions (1) to (4) at a high degree. The related literature mentioned above is incorporated into this specification as a reference.